welding gun amperage rating

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Good morning all ,I have a perfectly good 15 foot 400 amp tweco gun on my spoolmate 200.A friend just gave me a brand new 200 amp k@k bernard style gun 12 footthat is very light and comfortable.My machine is rated for 200 amps at 28 volts at 60% duty cycle and will put out 250 amps at 39 volts at 30% duty cycle.My question is will the 200 amp gun be plenty for most welding on my machine and how are the guns rated,I.E. will things start burning up if the amperage rating is exceded?              Felon  ps im keeping both gunsCaution lurker lives here" hmmm That is serious,pass the ganja and pick up a  24 of MGD"
Reply:Guns are rated using carbon dioxide gas.  The cooling effect of the gas is lost when you use an argon mix.  As a result you must derate the gun.  The 200 amp lighter gun would likely just do fine unless you are in a production shop running 150 to 200 amps eight hours a day.  From your description your machine can only do 100 %  duty cycle around 150 amps.  Derating is usually around 60% when using argon mixes.  The first signs of overheating is the contact tips not lasting and next is the wire sticking or jamming in the partially melted tip.  The gun gets quite warm.  The gun and lead do not suddenly  reach end of life in fire and smoke so there are many warning signs.
Reply:Lotechman        You are right on in the 100% at 150 amps.I use an argon mix but  not a production shop so I should be good to go with the small gun,and if I need the extra power I will  switch to the tweco gun.I was using co2 but like the prettier welds with mixed ,did not know about the co2 method of rating or its cooling characteristics,I must read up on the welding basics to enlighten myself.                    Thanks FelonCaution lurker lives here" hmmm That is serious,pass the ganja and pick up a  24 of MGD"